Invasive mussels

Overview

Figure 1. Irrigated agricultural lands within the U.S. potentially receiving Colorado River water, both inside and outside of the physical basin, are shown in yellow. Some of these irrigated lands may receive non-tributary groundwater, or water from tributaries not administratively treated as Colorado River water, such as from the Gila River. Irrigated lands in Mexico, totaling about 0.5 million acres, are not shown. Irrigated acreage is mapped from the 2011 National Land Cover Database. (Source: Moving Forward Phase 1 Report, 2015.)

Two related species of freshwater mollusks, quagga mussels (Dreissena bugensis) and zebra mussels (Dreissena polymorpha), have been introduced to the Colorado River basin and are currently identified as invasive species. These species, likely introduced by accident to Lake Mead 2007, have spread quickly throughout Lake Mead, Lake Powell, and the Colorado River below Lake Mead. Both larvae (veliger) and adult mussel forms can be transported on boat surfaces and contaminate water bodies.

Attaching themselves to surfaces by the thousands (Figure 1), the invasive mussels clog, biofoul, and otherwise impair water and power infrastructure. Invasive mussels also degrade recreational opportunities in infested water bodies and rivers, can impair propellor use, and lead to time-consuming boat inspections. In the process of filter-feeding, quagga and zebra mussels filter large volumes of water–about 1 liter/day per individual–which disrupts the aquatic food web by decreasing the availability of zooplankton and algae for native species, and increasing water clarity–which, counterintuitively, can contribute to proliferation of aquatic weeds.

Monitoring efforts of invasive mollusks and crustaceans include both counts of adult individuals and eDNA analyses. Reclamation collects water samples from water bodies across the western states, including water bodies in the Colorado River, which are analyzed with microscopy to detect veligers and molecular methods to detect the presence of mussels using eDNA. These monitoring results are collated in the Reclamation RISE database.

Quagga Mussels

Originally from Eastern Europe, the quagga mussel is a small (< 1.5” ) freshwater mollusk with white to yellow coloration. Quagga mussels reproduce prolifically and are difficult to eradicate. Quagga mussels were first found in the Colorado River Basin in 2007 in Lake Mead, Lake Mohave, and Lake Havasu. In 2012, quagga mussels were found in Lake Powell. Quagga mussels now live throughout the Colorado River system below Lake Mead, including the Central Arizona Project and all infrastructure in California receiving raw Colorado River water. There is much concern about quagga mussels spreading in the Upper asin beyond Lake Powell. While self-sustaining populations have so far failed to establish, individual mussels have been found in Lake Granby, Grand Lake, Shadow Mountain Reservoir, Willow Creek Reservoir, , Blue Mesa Reservoir, and Green Mountain Reservoir. Quagga mussels have some predators in the Colorado River system such as the Redear sunfish, which lives in parts of the Colorado River basin including Lake Havasu and below Davis Dam. These predators offer both an opportunity for some form of biologic population control and a potential mechanism for toxins and microorganisms found in quagga mussels to move up the food chain.

Data and tools

Reclamation RISE Database

Reclamation’s RISE database includes invasive mussel count and monitoring data from reservoirs and river reaches with infestations; enter “mussel” in the search bar.

Additional resources

NPS Glen Canyon Mussel Updates

The Glen Canyon National Recreation Area maintains mussel updates on its website, including current watercraft decontamination strategies and requirements.

Invasive Mussel Collaborative

The Invasive Mussel Collaborative collates ongoing prevention and removal projects across the United States, including several which extend through parts of the Colorado River basin.